Whether you’re losing weight, body building, or working out to stay healthy, knowing your lean body mass (LBM) can help you keep track of your goals and your health. Your lean body mass is how much you weigh if you subtract all your weight that comes from fat (your body fat percentage) from your total weight. You generally want to keep your lean body mass the same while you lose weight, so that the weight you lose is all from fat.[1] To determine your lean body mass and keep track of your fitness progress, you might first need to determine your body fat percentage. Other methods to estimate or determine your LBM vary in accuracy and accessibility, so choose the option that’s best for you. Maintaining your lean body mass will also help keep your bones strong and keep your fat levels to a healthy level that maintains brain and organ function.

Steps

Method1

Applying Calculations and Measurements

1

Calculate your LBM using your height and weight. Though not a perfect measurement, you can calculate a good estimate of your body fat percentage just using a formula with your height and weight. Enter your weight in kilograms for “W” and your height in centimeters for “H” into this equation to get your lean body mass (in kg):[2]

Men: Lean body mass = (0.32810 × W) + (0.33929 × H) − 29.5336

For women: Lean body mass = (0.29569 × W) + (0.41813 × H) − 43.2933

Note: 1lb = 0.453592kg, and 1in = 2.54cm

You can also go the easy route and use an online calculator like this one here.

2

Calculate your LBM from your body fat percentage. Use a technique listed below to determine your body fat percentage. Divide your percent body fat by 100 to make it a decimal, then multiply that by your total weight. For instance, if you weigh 200 pounds and have learned that your body fat percentage is 20%, multiply 200 x 0.20. This is your fat in pounds (200 x 0.20 = 40 lbs). Subtract that from your total weight to get your lean body mass; in this case, 200 - 40 = 160lbs of lean body mass!

It doesn’t matter if you calculate your weight using pounds or kilograms as long as you use the same measurement throughout your calculations.

3

Learn your body fat percentage from a skin fold assessment. A skilled practitioner can estimate your body fat percentage by pinching three, four, or seven different parts of your body and measuring the skinfold thickness with calipers. Learn your body fat percentage by plugging these numbers into a formula or using a conversion table.[3] This is a relatively inexpensive option, but the results may not be very accurate.[4]

Some trainers at the gym, personal trainers, or sports therapists may be skilled in this technique. Find someone who does it often and knows how - check at your gym!

Method2

Utilizing Technology

1

Use a bioelectrical impedance scale. You may have seen a bioelectrical impedance scale at your gym or personal trainer’s office. These scales have electrodes you stand on, and they send gentle electricity through your body to measure your body fat percentage (fat and muscle conduct electricity differently).[5] They are safe and you don’t feel a thing. Simply stand barefoot on the scale and follow the instructions.

Some scales will tell you your LBM directly, though most will probably just determine your body fat percentage.

You can purchase one of these scales to use at home to keep track of your body fat percentage over time.

This is an easy-to-use method, but is not always very accurate.

2

Pursue hydrostatic weighing. Hydrostatic, or underwater, weighing compares your weight on land to your weight while completely submerged in water. A skilled technician can then calculate your body fat percentage. This is a very accurate method, but it can cost between $40-60 on average. Find a research lab or performance center who does underwater weighing near you.[6]

A “bod pod” (or air displacement plethysmography machine) is similar to hydrostatic weighing, except it uses air instead of water. It is pretty accurate when testing people who are close to a healthy BMI, though may be less accurate for very lean people.[7] Research your area to find one near you.

3

Get a DEXA scan. A dual-energy x-ray absorptiometry (DEXA) scanner is used like an x-ray – it’s a harmless and very accurate, though probably expensive, procedure. It is usually used to measure bone density and monitor osteoporosis. This is a very accurate option, but you have to see a medical professional that provides DEXA scans. It may also be expensive.[8] Talk to your family doctor for more information.